A user terminal such as a personal computer (PC) or a smartphone supports a chat service between users through a messenger program. With the development of a messenger service, a security technology that encrypts chat contents has been also developed such that the third party except chat counterparts does not confirm the chat contents. For example, a technology that encrypts the chat contents by using a symmetric key or an asymmetric key may be used. Moreover, an end-to-end encryption technology that performs encryption/decryption at a terminal is used such that the chat contents are not disclosed when a message is sent from the terminal to another terminal.
A user utilizes a plurality of terminals with one user account, and thus the possibility that chat contents are disclosed increases. For example, even though a user chats by using a messenger application of a smartphone, the chat contents are displayed on a PC or tablet (which is placed at a location different from that of a user) in which the same messenger application is installed.
As such, in the case where a user utilizes a plurality of terminals, a current manner in which the chat contents are synchronized with and provided to the plurality of terminals is vulnerable to the security.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present disclosure.